One man who was not caught out was the team's Austrian billionaire owner Dietrich Mateschitz, who said he had known for some time - a sign of possible fault lines within a team divided by its drivers.

"We knew about Mark's decision for some time and I think it's a very good one with benefits for him and Porsche," Mateschitz said, adding that Webber had flown to Austria earlier in the week for talks.

Rule changes for 2014 central to his decision

Speculation linking Webber to Porsche first surfaced months ago, with the Australian quick to pour cold water on them at the time, and he validated them finally.

"The decision has been there for quite a long time for me actually. So, I've known for quite a while, I've had a plan and I've stuck to it," the 36-year-old told reporters.

"Dietrich has been completely up to speed with my thinking in the last six to eight months."

It was a Porsche announcement. I informed Christian before the announcement, which contractually I should do, so that's what we did. It was about Porsche and Mark Webber today."

Mark Webber

Webber said the rule changes for 2014, when a new V6 engine is introduced, had played a part in his decision but he has also been complaining for much of this season about the current situation with tyres that do not allow him to race flat out.

"There's lots of reasons that come into the pot, I think, when any sportsman or women comes to that time in their career where they want to call it a day," he added.

"There's going to be big, big changes in this sport next year, so I may as well go and do those big, big changes where my future is going to be."

Webber said he would be fully motivated and committed right to the end of the season in Brazil and Horner expected no less from the driver.

Other drivers felt he was doing the right thing.

"I think he'll have a lot of fun behind the wheel, as he's doing now, with a little bit less problems outside the wheel than we have now in Formula One," said Ferrari's Fernando Alonso.

"With the new series I think he will have a little bit more fun and I wish him the best of luck for the rest of the championship and for the future."

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